Originally Posted by ColdCase
Brake traction control will keep them from spinning much, and transfer power to the tires with traction. The biggest limitation to QTII is that it needs wheel spin for traction control to work and brake traction control sucks up a good bit of power (its hard on brakes in the really rough stuff).
Its not relative to normal street use, but when you hammer the throttle, the QD system locks the rear axle to maximize traction. QT has to wait till a tire loses traction and lock that wheel, until the other looses traction.... then lock that one.. not that anyone but a STR8 driver would want to stomp on the throttle to impress the girls... or need that extra second in the quarter mile
You are correct in describing the need for tire spin to engage the brake lock differential. But from that to elevating Quadra Drive II to the status of God's gift to mankind (which is exclusively reserved for BMW) is a stretch. Speaking of which the BMW variant of Electronic Brake Differential Lock works amazingly well in snowstorms. At least on the 335i (rear drive). QD2 is a superior system in extreme conditions; it doesn't make the car any safer or capable in day to day driving challenges. in addition, I do not think SRTs have Quadra Drive 2 but maybe they do but it's named differently.